There is just not that much info being sent to the rears in most movies. Mostly it is environmental effects (rain, cars, birds, etc) in most cases. Some movies offer more in terms of surround. It would be rather distracting if there was a noticeable amount of sound and info coming from behind or the side all the way through a movie.
As far as using full range rears, it really is unnecessary in movies. I can't think of too many instances when 30Hz or lower info is called for. Besides, anything really low is pretty omnidirectional and your sub should pick up the
slack. You may benefit from full range speakers in the rear if you like surround sound music and use 5+ channel stereo or such.
Hang in there, sometimes the hype and anticipation can make a great speaker sound average.
